Combustion device for liquid fuel



May 30, 1961 A. R. BOELSMA COMBUSTION DEVICE FOR LIQUID FUEL Filed Feb. 26, 1958 l K a INVENTORI A. R. BOELSMA BY:

HIS ATTORNEY United States Patent COMBUSTION DEVICE FOR LIQUID FUEL Aaldert R. Boelsma, Delft, Netherlands, assignor to Shell Oil Company, a corporation of Delaware Filed Feb. 26, 1958, Ser. No. 717,601 Claims priority, application Belgium 'Feb. '28, 1957 H 2 Claims. (Cl. 158-4) This invention relates to a device for burning liquid fuel, particularly heavy fuels, such as viscous residual oils including tars and asphalt. US. Patent 2,806,517 discloses a combustion device for liquid fuel comprising an air chamber, and a combustion chamber made of refractory material, both of which are substantially formed as cylinders of revolution around a common axis and connected together by a centrally located opening of a reduced diameter with respect to the diamter of both chambers, an atomizer for liquid fuel being centrally located in the air chamber, which atomizer sprays the fuel in the form of a hollow cone through the said opening into the combustion chamber, in such a way that the fuel enters the combustion chamber near the edge of the said opening, the air chamber being provided at the periphery with tangential air supply openings.

In a combustion device of this type a part of the ash present in the fuel to a slight extent collects in the conventional horizontal design in the bottom part of the combustion chamber in the form of molten slag. The latter then solidifies in situ or flows to the firing space adjoining the combustion chamber where it subsequently solidifies. The amount is usually so slight that during normal inspection of this combustion device the solidified slag can be removed and no difliculties occur during operation.

If, however, it is desired to assemble such a device vertically, viz. with the opening of the combustion chamber directed upward, difliculties may be anticipated with this known device since there is then a risk of the molten slag flowing towards the narrowed opening between air chamber and combustion chamber and at least partially blocking this opening or the burner nozzle and consequently interfering with the combustion.

-When ash-containing residual liquid fuel is used in a combustion device of this type there may be the drawback that the refractory lining of the combustion chamber is adversely affected by the ash depositing on the wall approximately half-way the length of the chamber. At the high temperature of approximately 1600 C. this ash attacks the lining and together with unburnt or partially burnt fuel particles, flung against the wall, may cause coke formation.

The invention now provides an improvement of the above-mentioned combustion device obviating these drawbacks. According to the invention the improvement consists in that the combustion chamber is provided at the periphery near the end adjoining the air chamber with an annular slot, which is defined by axial or substantially axial planes and is connected to an air supply line through which secondary air may be passed along the peripheral wall of the combustion chamber into the said combustion chamber. According to the invention the said annular slot may be provided with guiding members imparting to the secondary air a peripheral motion in the same direction as the motion of the centrally supplied primary air, preferably in such a way that the speed of rotation of the secondary air is of the same order of magnitude as the speed of rotation of the mass of flames formed by means I test flame gases and the ash particles and any soot particles which are flung out from these gases; this secondary air then takes part in the combustion. Nor does this manner of introduction prevent the formation of the outer external toroidal whirl, as described in US. Patent 2,806,517, near the bottom of the combustion chamber which is desirable for a good operation. For a good operation of the combustion device it is desirable for the total quantityof primary plus secondary air to correspond as much as possible to the quantity of combustion air theoretically required for the fuel.

A special advantage 'of the combustion device according to the invention is that the said slot for the secondary air enables the actual burner and air supply members to be designed as a single, easily detachable bottom part, so that after removal of this part the combustion chamber is readily accessible.

A correct choice of the flow resistances of the two air supply lines which may be connected to the same air supply makes it possible to control the quantities of primary and secondary air in such a way that these are preferably approximately equal, since the ratio of the quantity of air supplied directly around the atomizer and that supplied at of centrally supplied air is too small in proportion to the quantity supplied at the periphery, a flame is formed having a tendency to smoke; moreover there is then a risk of the said external toroidal whirl being disturbed, as a result of which the ignition of the fuel-air mixture is jeopardized. Conversely, if the quantity of peripheral air supplied is proportionately small the object is not achieved, or only insufiiciently, and there is a danger of ash or coke being deposited on the wall of the combustion chamber.

In an air box communicating with the air chamber, a plurality of concentric cylindrical partitions are preferably fitted co-axially with the chamber in order to ensure a uniform distribution of the air in all directions over the pe riphery of the chamber.

The invention will now be further illustrated with reference to the drawing showing a combustion device according to the invention, wherein:

Fig. 1 is a vertical sectional view of the device.

Fig. 2 is a vertical sectional view along line 2-2 of Fig. 1 showing the inclination of the blades 8 in the peripheral slot 3.

Fig. 3 is a vertical sectional view along the line 3-3 of Fig. 1 showing the inclination of the blades 6 in the central part of the air box 7.

Referring to the drawing, 1 is the combustion chamber to which fuel and primary air are supplied via the opening or throat 2. Secondary air is supplied at the periphery via the slot 3. The atomizer burner 4 through which liquid fuel may be supplied (via connection 10) is arranged centrally in the air chamber 5. A connection 9 is also provided by means of which it is also possible to supply gaseous fuel via a channel around the atomizer holder to the combustion chamber. The primary air passes via blades 6 from the'air box 7 into the air chamber 5. The slot 3 is provided with a plurality, e.g. 18, of blades 8 distributed over the entire periphery at such an angle that a rotary motion is imparted to the secondary air by the blades 8 in the same direction as is imparted to the primary air by the blades 6.

The air box 7 opposite the combustion chamber 1 is closed by a cover 11 secured to the air box 7 by means of a flange 112 and supports both the actual burner 4 with the air-supply members and the bottom 13 of the combustion chamber, the latter by means of the rods 14 and the plate 15. Around the bottom 13 is the annular slot 3 for the secondary combustion air, in which slot are arranged the inclined blades in order to impart the required rotary motion to this air. Both the secondary air and the primary air which rotates around the burner nozzle and is introduced into the combustion chamber comes from the same air box; the object of the cylindrical partitions 16 and 17 is to provide a uniform distribution of the air in all directions. The dimensions of the air supply members are such that the quantities of and secondary air are approximately equal. A substantial part of the secondary air gives rise to combustion near the open side only of the combustion chamber.

It will be manifest that after unfastening the flange 12 and if necessary, fuel lines connected to the burner, the bottom 13 of the combustion chamber can be removed, giving access to the refractory lining of the combustion chamber for the purpose of inspection and repair without the necessity of entering the furnace. Thus, if inspection or the like is required when the furnace is hot, it is consequently not necessary to wait until it has cooled down sufliciently, and this effects a considerable time-saving.

In the device according to the invention there is no danger of pieces of coke broken away from the wall, caked ash or the like finding their way on to the atomizer or the opening for the primary or secondary air, since even if ashcontaining residual fuel is used, the formation of deposits on the wall of the combustion chamber is entirely pre vented.

The combustion device according to the invention is therefore particularly suitable for vertical mounting, especially with upward movement of the flame gases.

A special advantage of the device according to the invention is that for a certain capacity a smaller air chamber is required than when all the combustion air is supplied centrally via the air chamber. This results in a design which is lighter and more easy to handle.

The combustion device according to the invention is therefore also admirably suited for vertical mounting since the air box is simple to assemble and disassemble, and consequently the box can be supported in a simple manner.

When the combustion device is operating a flame pattern is obtained in which an external toroidal whirl 18 and aninternal toroidal whirl19 can be distinguished. In addition to these whirls there is also a rotary peripheral motion.

The external whirl 18 ensures that the mixture of fuel and primary air emerging from the throat 2 into the combustion chamber is rapidly ignited.

I claim as my invention: 1

1. A combustion device for viscous residual oils com prising an air chamber, a horizontally mounted refractorylined wall, said wall having a shallow upwardly opening dish-shaped upper surface, a vertically mounted refractory-lined wall of uniform thickness extending upwardly from the horizontal wall a distance substantially greater than the thickness of the horizontal wall, said walls forming a combustion chamber, said combustion chamber being vertically mounted above said air chamber, said chambers being substantially formed as cylinders of revolution around a common axis and connected together end-to-end by a centrally located opening of reduced diameter with respect to the diameters of both chambers, atomizer means for viscous residual oils axially located in the air chamber adjacent said central opening and arranged to spray residual oil upwardly and outwardly in the form of a hollow cone passing through said opening into the combination chamber near the edge of said opening and over said dish-shaped surface to produce an outer toroidal whirl, a cylindrical air box of substantially the same diameter as said combustion chamber below and adjacent the base of said air chamber and in communication therewith, said air chamber being provided at the periphery of the base thereof with spaced downwardly extending vertical blades centrally positioned in the air box to form tangential air supply openings for primary air, the lower end of said vertically mounted wall being uniformly spaced laterally from the periphery of said horizontally mounted wall to provide an annular narrow slot-like opening, said annular slot-like opening having inclined blades therein and being in communication with said air box whereby secondary air may be directed along the entire inside face of said vertically mounted wall and an internal toroidal whirl produced so that the formation of molten slag and coke normally produced by the combustion of viscous residual oil avoided.

2. A combustion device for viscous residual oils as defined in claim 1, in which the effective areas of said cen trally located opening and said annular slot-like opening into the combustion chamber produce such flow resistances that the ratio of the quantities of air passing through the openings is between 1:2 and 2:1.

References Cited in the file of this patent UNITED STATES PATENTS 1,172,755 Wilson Feb. 22, 1916 2,673,726 Oldenkamp Mar. 30, 1954 FOREIGN PATENTS 729,361 Great Britain May 4, 1955 459,326 Italy Sept. 5, 1950 

